This invention relates to wheel anti-rotation means and, more particularly, to an auxiliary means for restraining a wheel against rotation with respect to a shaft and/or other wheels secured to the shaft when a primary means for securing the wheel to the shaft is disturbed. Related to the present invention is U.S. Pat. No. 4,497,612--Knorowski et al which is incorporated herein by reference thereto.
The invention will be described as it may be applied to a steam turbine. However, the invention may be used with any type of rotating machinery wherein it is desired to provide an auxiliary or backup means for securing a wheel against undesirable rotation with respect to a shaft to which it is secured and/or with respect to other wheels secured to the shaft.
Some steam turbines utilize rotors wherein the turbine wheels that carry turbine blades at their radially outermost portions are not an integral part of the shaft of the rotor. In addition to the turbine blades, each wheel includes a hub section generally disposed at its radially inward portion which has a bore therethrough for receiving the shaft of the rotor. Typically the wheel may be secured to the shaft of the rotor by an interference shrink fit between the radially inner surface of the hub section defining the bore and a corresponding peripheral surface of the shaft. During normal turbine operations, this interference fit prevents rotation of the wheel with respect to the shaft and/or other wheels secured to the shaft.
In order to maintain efficiency and mechanical integrity of the turbine, it is necessary that the wheels, and thereby the turbine blades, be maintained at a substantially fixed position relative to the shaft and relative to other wheels secured to the shaft. This requirement should be met during all turbine operations, including normal but non-steady state conditions, such as overspeed and undesirable thermal transient periods. To ensure that the turbine wheels do not rotate relative to the shaft and/or other wheels secured to the shaft during such turbine operations, anti-rotation means may be included with the shaft for augmenting the primary means, such as an interference shrink fit, for securing a wheel to the shaft and for inhibiting rotation of a wheel with respect to the shaft and/or other wheels secured to the shaft should the primary securing means loosen or be otherwise compromised.
One system for providing auxiliary means for securing a wheel to a shaft is disclosed and claimed in the aforementioned U.S. Pat. No. 4,497,612--Knorowski et al, which is assigned to the present assignee. One of the features of the system of the Knorowski et al patent is an axially extending groove cut into the periphery of the shaft. In certain applications, it may be desirable not to have to machine the peripheral surface of the shaft to include this axial groove. In addition, as discussed in detail in the Knorowski et al patent, any anti-rotation means to be used should minimize stresses in the wheel, shaft and anti-rotation means itself.
Accordingly, it is an object of the present invention to provide anti-rotation means for securing a wheel against undesirable rotation with respect to the shaft and/or other wheels secured to the shaft without having to fabricate an axially extending groove in the periphery of the shaft.
Another object of the present invention is to provide anti-rotation means in which stress concentration factors in the anti-rotation means and in the region around the anti-rotation means and the shaft is minimized.